Osteoporosis and Fracture Prevention

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One in three women and one in twelve men over the age of 50 develop osteoporosis. Osteoporosis predisposes to bone fractures, of which there are over 200,000 per year in the UK. In young adulthood, natural bone formation is the equivalent to that which is resorbed, maintaining the status quo of the fully formed skeleton. With ageing, bone formation lags behind resorption, and this net loss results in osteoporosis. The underlying condition is due to a lack of mineralisation of calcium within the bone, making it more likely to fracture than normal bone. Clinical decision making on optimum ways to prevent and treat osteoporosis can be made by measurement of bone mineral density. Progress on treatment can be monitored with sequential bone density studies. These results are usually expressed as the variation of an individual’s reading from the normal average. There is an increased risk of bone fractures when the bone mineral density is one standard deviation below the normal age-related average. Other risk factors include a maternal history of hip fracture, low body weight (body mass index below 19kgs/m2), early menopause (below 45 years of age), steroid treatment, and a previous personal history of thin bone related fractures.

Measurement of bone density

Bone mineral density (BMD) is expressed as a T-score and a Z-score. The T-score is calculated from the variation (the standard deviation) between an individual’s measured BMD and the mean BMD of matched healthy young adults. A T-score of less than

-2.5 at the spine, hip or forearm is classified as osteoporosis. Lesser degrees of bone thinning is termed osteopaenia.

The Z-score is a measure of variation (standard deviation) from healthy patients of the same age range as the test patient. Z-scores do not give a diagnosis of osteoporosis but provide a fracture risk in relation to the population. Each Z-score unit of -1 is associated with a two fold increase in fracture risk.

Dietary factors

Bone and calcium metabolism are intricately related. Calcium in turn is dependent on Vitamin D for absorption. The main sources of calcium are dairy products and green vegetables. Absorption of calcium may be reduced by bran and bran-based cereals. Vitamin D is made in the skin following sun exposure and the main dietary sources are from foods such as margarine, breakfast cereals, oily fish, meat and eggs.

Dietary factors therefore have an important role to play in healthy living. A healthy bone mass is also maintained with regular exercise. A varied diet should contain adequate calcium of at least 100mg per day for most adults. An exercise programme with brisk walking for about thirty minutes, five days a week, helps maintain and protect bone mass. Heavy alcohol drinking is associated with lowering of bone mineral mass. There is no clear relationship between smoking habit and fracture risk.

Dietary phyto-oestrogens are found in tofu and soya milk, lentils, sunflower and pumpkin seeds. Biochemically, these are similar to normal animal oestrogens and are thought to have a protective effect against bone loss. There are no scientific studies, however, to define the exact role of phyto-oestrogen use in the prevention of osteoporosis and fractures.

Biphosphonates

Biphosphonates are drugs that reduce the breakdown of bone and therefore maintain bone mass. Examples of available preparations are Fosamax (alendronate sodium), Didronel (disodium etidronate), Bonefos (sodium clodronate) and Actonel (risedronate sodium). There are many other biphosphonate drug preparations and these are all available by prescription only. The side effects of biphosphonates include gastrointestinal disturbances (nausea, diarrhoea, constipation, and abdominal pain), headache and rarely ‘flu-like symptoms. Biphosphonates on their own have been shown to reduce the risk of osteoporosis as well as to help stabilise and reverse established osteoporosis. It is important that directions for dosage and how the medicine is taken are closely followed to optimise absorption and efficacy of the tablets.

Hormone replacement therapy

Hormone replacement therapy (HRT) in post-menopausal women involves prescription of an oestrogen or oestrogen-like compound. In women who have their uterus intact (i.e. those who have not had a hysterectomy), a progestogen is needed in addition to the oestrogen. In post-menopausal women, oestrogen levels are very low and oestrogen supplementation is used to treat osteoporosis or osteoporosis risk. HRT has been shown to prevent osteoporosis and to reverse established disease. HRT is also indicated where there are menopausal symptoms such as flushing and sweating and vaginal dryness. There is, as yet, no proven benefit of HRT in protecting the cardiovascular system from clogging or brain from dementia. There are side-effects of HRT and these must be discussed with your doctor. These include thickening of the lining of the womb, growth of fibroids, endometrial cancer, deep vein thrombosis and breast cancer. The serious adverse effects of HRT, including cancer risks, are fortunately rare.

Most HRT preparations contain oestrogen that are either synthesised from laboratories or extracted from animal products. Newer, more directed agents called selective oestrogen receptor modulators (SERMS) have been developed. An example of this is Raloxifene (Evista). These are specially synthesised chemical derivatives that aim to give the best benefits of HRT from the oestrogen-like molecule without the adverse effects. Raloxifene has a protective effect on bone mass and has less of an effect on breasts, therefore potentially reducing breast cancer risk. There are some studies that suggest that Raloxifene might have a role in preventing breast cancer but this is being studied in larger clinical trials. The results of these trials are awaited with interest. Other HRT agents which are not in themselves oestrogen, include tibolone (Livial). These newer drugs are also thought to be effective hormone replacement treatments that have less of an effect on the breast. The optimum choice of which hormone replacement therapy is best for you should be discussed with your doctor.

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